A memory system having a volatile memory such as a DRAM built therein maintains data in the volatile memory by supplying power to the volatile memory from an external power supply.
However, there are cases where power cannot be supplied from an external power supply to the volatile memory such as a case where the memory system is operated in a low power consumption mode and a case where supply of power from an external power supply is cut off. In such cases, a structure for preventing loss of data stored in the volatile memory is necessary.